Even best-in-class GNSS and cellular antennas can’t overcome integration that undermines their capabilities. Here are four top pitfalls to avoid when designing a device — all based on real-world products that Taoglas engineers have helped optimize.
The PCB is Too Small, the Wrong Shape, or Both
The Problem: Small and irregularly shaped PCBs are a fact of life with many devices, particularly IoT products such as asset trackers and wearables. Placing a patch antenna on a PCB that is irregularly shaped and/or that is too small to provide a sufficient ground plane disrupts the current flow. These constraints negatively impact key parameters like the axial ratio, leading to unreliable signal reception. Mounting a patch antenna in the corner of the PCB can destabilize its performance by disrupting the optimal ground plane currents.
Chip antennas, meanwhile, rely heavily on the PCB’s ground plane to function as a resonant structure. A ground plane that is too small will severely degrade its efficiency and bandwidth.
The Solution: For both patches and chips, always design for the ground plane size and shape specified in the antenna’s integration guide for optimal performance. For example, the Taoglas WLA.04’s integration guide recommends placing it mid-point on the long side of the PCB with a minimum ground plane of 90×50 mm.
More Tips: See “Why Antenna Placement on PCBs is Critical for Chip Antenna Radiation Performance” and “Understanding Ground Planes for Cellular and GNSS Devices.”
Insufficient Keep-Out Area and Metal Proximity
The Problem: Placing the antenna too close to other components, metal shields, or batteries detunes it and blocks signals. This lack of a proper “keep-out” area is a frequent cause of failure.
The Solution: Follow the antenna’s integration guide to ensure an adequate keep-out area. For example, Taoglas recommends keeping the antenna a minimum of 20 mm from the battery. And don’t overlook proximity to screws, cables, and copper traces, which all can undermine radiated signals.
Of course, this is easier said than done in devices where everything has to be shoehorned in to meet svelte form factor requirements, such as pet trackers. One solution is to choose the smallest antenna that will meet product and performance requirement. An example is the Taoglas PCS.62.A antenna, which is designed for sub-6 GHz cellular applications. At just 38 x 10.3 x 3 mm, this ultra-compact antenna increases design flexibility simply because it takes up less board space.
More Tips: See “Top Tips for Ensuring Your PCB Maximizes Antenna and Application Performance.”
Enclosure Interference with Patch Antennas
The Problem: When a device enclosure is placed flush against the top of a patch antenna, it creates a dielectric gap that detunes the antenna, shifting its frequency and reducing gain.
The Solution: Follow the antenna’s integration guide for the required air gap between the antenna radiator and the enclosure in your mechanical design (allow more than 2mm gap). In some cases, a custom antenna might be the only option, such as when the form factor design is already locked down.
This option also applies to other types of antennas. For example, Taoglas designed a custom flexible GNSS antenna to fit the unique form factor of Absolute Cycling’s The One cycling computer. The custom Taoglas FXP614.A was the only way to achieve The One’s demanding performance requirements such as gradient and altitude accuracy. To learn more, see “Customized GNSS Antenna Enables Absolute Cycling’s The One Cycling Computer to Balance a Sleek Design with High Performance.”
Mismatched Transmission Lines
The Problem: Using a poorly designed transmission line that isn’t matched to 50 ohms results in significant power loss due to signal reflection. This is often an afterthought for designers.
The Solution: Impedance matching ensures that the antenna can broadcast all of the signal that the transmitter provides. This also maximizes battery life because the transmitter isn’t wasting power that literally goes nowhere because it’s reflected.
In the case of cellular, proper impedance matching also is key for achieving certification by the Federal Communications Commission (FCC) and by each mobile operator whose network it will use.
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